Depending on the type of lung cancer, surgery, chemotherapy, and/or radiation therapy are the main stays of therapy. There are no studies that have definitively determined that cannabis is beneficial for lung cancer, and it is recommended that any therapy you are considering be discussed with your oncologist. It should go without saying that you should not smoke anything, including medical marijuana, due to your condition.
Cannabis in-vitro has been shown to have to have anti-tumor properties and may be beneficial as a supplementary therapy for cancer in general, although much more human research will be necessary to determine if this is actually the case.
On the other hand, much research has been done to demonstrate that cannabis is helpful for the treatment of side effects due to chemotherapy and radiation therapy, especially for nausea and vomiting. Cannabis is also helpful for the management of pain from a variety of different medical causes.